H7N9: Historical prevalence and distribution of H7N9 among wild birds

Source: Posted by Ian M Mackay on Virology Down under. CDC Emerging Infectious Diseases published a paper (Volume 19, Number 12—December 2013) on the Historical Prevalence and Distribution of Avian Influenza Virus A(H7N9) among Wild Birds. A very interesting document, it provides a better understanding on transmission of H7N9 under wild birds.

In this paper, the authors reviewed 48 published studies that listed findings of influenza A virus haemagglutin type H7, or neuramonase N9 viruses as well as H9N2. The prevalence was calculated as the number of positive samples divided by the by number tested.

H7N9 has been rarely reported from Delaware (USA), Alberta (Canada), Guatemala, Spain, Egypt, Mongolia and Taiwan but has not been reported from Russia, Japan, South Korea or China from birds sampled between 1976-2012.

The outcome? If you were planning wild bird surveillance to track H7N9 spread in these non-poultry animals, you’ll need to sample >30,000 wild birds to find 1 positive for H7N9 (its Asian prevalence was 0.00931%).

That’s a rare bird.
This is just a rough gauge of course because it is entirely dependent on when, where and how thoroughly bird populations were sampled, how they were sampled, what they were tested with and how the sequencing methods performed. It also focuses on HA and NA genes, at the expense of other internal influenza gene segments which also have an important role in the assemblage of new viruses.

Related links to this topic published by FAO-USGS on Avian Influenza Projects related to migrating birds: